The present invention generally relates to removing contamination from the surface of substrates used in the fabrication of micro electronic devices. In particular, the invention relates to the use of methods and apparatus for removing residual organic contamination from the surfaces of such substrates using ozone so as to prepare the substrates for further processing in a manner which is more efficient and effective than is presently implemented.
A variety of processes are known and are presently used in the microelectronics industry for cleaning surfaces of substrates. Cleaning processes and surface preparation are required in micro electronic device manufacturing as it is essential to ensure a contamination-free surface before subsequent processing steps can be performed on substrates. In the micro electronic industry today, these contaminants are removed by a variety of processes including plasma ashing and UV/ozone processes. Plasma ashing seems to be the most popular method used in the industry whereas existing UV/ozone and heat/ozone processes are also used only if the substrates to be treated can be positioned close to the UV emission so as to generate the ozone adjacent to the part to be treated. The characteristics of the present cleaning systems reduce them to use in a batch mode and as a result, a limited number of substrates can be treated over a period of time.
Plasma cleaning, also known as glow discharge cleaning, is a process performed with reactive ionized gas in order to obtain an appropriate surface on the substrate before other operations such as plating or masking can be introduced. This process results in chemical reactions without the need of exposing the surfaces to high temperatures. To produce the volatile atmosphere, typically molecular gases including oxygen, are flowed into the chamber and are dissociated to varying degrees in the plasma generated by the application of RF or microwave energy. A chemically active mixture of electrons, ions and free radicals are generated with photon energy being emitted when excited particles lose energy in transit to a lower energy state. As a result, the part or substrate to be cleaned is processed by a combination of physical effects including ion bombardment and chemical processes which react with contamination existing on the surface of the substrate in the form of carbon to produce products such as residual surface ash and CO and CO2 and H2O.
The use of the combination of ultraviolet rays and ozone is widely used today in methods for cleaning substrates and particularly as a pre-treatment of these surfaces before further processing by the use of polymers. An ozone producing lamp is placed adjacent to and within a few centimeters of the substrate to be cleaned or treated. The high energy light from the ultraviolet lamp produces atomic oxygen and ozone which reacts with contamination on the surface of the substrate in the form of carbon to produce products including CO and CO2 and H2O. This method has been found to be useful however the organic contaminant removal rate is relatively low if additional energy (heat) is not added to the process.
Representative examples and variations of the above summarized processes are contained in a number of prior art references. The following references are representative of the above prior art and are considered to be processes which are limited to the use of directly heating the items to be cleaned simultaneously with subjecting the items to ozone and none of which include a description of a continuous inline process of the nature of the invention as presented herein:
U.S. Pat. No. 5,762,755
U.S. Pat. No. 5,747,387
U.S. Pat. No. 5,709,754
U.S. Pat. No. 5,480,492
U.S. Pat. No. 5,228,206
U.S. Pat. No. 5,178,682
U.S. Pat. No. 5,044,314
Japanese Published Patent Application No. 3165028A
Japanese Published Patent Application No. 3088329A
Japanese Published Patent Application No. 3046225A
Japanese Published Patent Application No. 2106040A
Japanese Published Patent Application No. 6133529A
Japanese Published Patent Application No. 63099529A
Japanese Published Patent Application No. 61194830A
A representative explanation and the technical and scientific reasoning for the removal of organic contamination material from the surfaces of electronic devices using ozone is provided in the publication xe2x80x9cCritical Process Variables for UV-Ozone Etching of Photoresistxe2x80x9d, Peter C. Wood et al, Materials Research Society Symposium Proceedings, Volume 315, copyright 1993 Materials Research Society, pp. 237-242.
In some devices using ceramic substrates, a diffusion step is needed between two metals such as nickel, gold and molybdenum in order to ensure a good bond of the circuitry to the substrate. The prior art methods are not satisfactory in that case. It has been found that this diffusion step could result in organic stains on the ceramic and metallized surfaces. These stains originate as a result of such factors including the contamination in the atmosphere, the normal work environment, residual material from the resin remaining on the surface, and even fingerprints of humans when substrates are subsequently heated, for example, to carry out a diffusion step. In the manufacturing of flip chip assemblies, it may also be that any fibers or residual organic material on a substrate will result in carbon stains after solder reflow steps. It has been found that no matter how clean the atmosphere in the work environment there are usually resulting carbon stains on the surfaces of these substrates which could result in defective processing during subsequent steps. It is these types of carbon stains that have been found to be not effectively removed by known cleaning processes to which the subsequently described invention is primarily addressed. The invention has been found to be effective in the removal of these types of stains resulting from relatively high temperature processes and the invention can be thought of as a relatively mild cleaning procedure where carbon based stains are dissipated from the surface into vapor including CO, CO2 and H2O as opposed to the more robust high temperature etching procedures of the prior art which reduces the surface contamination to removable ash.
It is an object of the present invention to provide a new method and apparatus for removing contamination from the surfaces of substrates by the vaporization of the contamination.
It is a further object of the invention to provide for the removal of contamination at lower temperatures than are used in the prior art.
It is a further object of the invention to make use of ozone for the removal of contamination of the surface of substrates which does not require the addition of any heating or other energy in the ozone zone.
It is a further object of the invention to provide a method and apparatus for the continuous and inline removal of contamination from the surfaces of substrates.
It is a further object of the invention for the cleaning and treatment of surfaces of substrates where a plurality of substrates are involved and the substrates may be layered or tiered so that all surfaces of the substrates can be treated at the same time.
These and other objects and advantages of the present invention are apparent from the detailed description and the preferred embodiments which subsequently follows.
According to one aspect of the present invention, there is provided a process for removal of carbon based substances from the surfaces of one or more substrate. The process includes the step of transporting the substrates to a first zone where the substrates are heated to a temperature of at least 125xc2x0 C. The heated substrates are then transported to a second zone where the substrates are surrounded by an atmosphere containing ozone whereby the carbon based substances on the surfaces of the substrates are removed as vaporized products including CO, CO2 and H2O.
According to one aspect of the present invention, there is provided a continuous process for cleaning the surfaces of one or more substrates of organic contamination existing on the surfaces of the substrates. The process includes the steps of transporting the substrates to a first zone where the substrates are heated in a nitrogen environment to a temperature of at least 125xc2x0 C. The heated substrates are then transported to a second zone which is at room temperature where the substrates are surrounded by an atmosphere of ozone whereby the organic contamination on the surfaces is vaporized.
According to a further object of the invention, there is provided an apparatus for removal of carbon based substances from the surfaces of one or more substrates, comprising means for transporting the substrates to a first zone where the substrates are heated by heating means, to a temperature of at least 125xc2x0 C., and means for transporting the heated substrates to a second zone which includes means for surrounding the substrates with an atmosphere containing ozone, whereby the carbon based substances on the surfaces are vaporized.
According to a further object of the invention, there is provided apparatus for cleaning the surfaces of one or more substrates of organic contamination on the surfaces of the substrates. The apparatus includes means for transporting substrates through a first and a second chamber. The first chamber includes means for heating the substrates to a temperature of at least 125xc2x0 C., in a nitrogen environment. The second chamber, which is at room temperature, includes means for surrounding the substrate by an atmosphere of ozone whereby the organic contaminant on the surfaces thereof is vaporized into vapor products including CO, CO2 and H2O.